It is known to employ precipitated silica in combination with 0.3-3.0 weight % of a carboxylic acid or a derivative thereof for the heat stabilization of siloxane oils (Japanese Pat. No. 34868/76). These precipitated silicas, however, are not effective in diorganopolysiloxane elastomers such as heat hardening silicone rubber.
In German AS No. 1242866 there is described a composition of monazite sand corresponding to a rare earth oxide mixture for the heat stabilization of molding compositions based on diorganopolysiloxane elastomers. These molding compositions can also include reinforcing fillers such as silica dioxide sublimed form. The disadvantage of these mixed oxides are the intensive coloration of the elastomer, the high amount of additive of 16-40 parts by weight to 100 parts by weight of elastomer, the lack of fine particle size (about 50 microns) and the difficult dispersibility of the rare earth oxides, the surface spots brought about in films produced from the elastomer compositions.
In German AS No. 1230562 there is described the use of hydrophobized precipitated silica as antiaging agent.
German OS No. 2617434 described the employment of a mixture of pryogenically produced titanium dioxide and cerium (III) oxide as a heat stabilizer for diorganopolysiloxane elastomers.
In German OS No. 2727611 there is described a flame protected silicone rubber containing 0.1-3 parts by weight of cerium (IV) hydroxide